>> n_tty_read() checks the pending buffer and consume it before>> input_available_p().>> Why not move this _inside_ "input_available_p()"? There are only two > call-sites, and strictly speaking they both want it.

The only reason for me is this is just quick hack.

Yes, I guess the input_available_p() is preferable place than my patch.I'm still not checking the related path etc. deeply though.